HomeMy WebLinkAboutEngineer's OWTS Design PlanHuddleston-Berry
2789 Riverside Parkway
Grand Junction, Colorado 81501
Phone: 970-255-8005
Info@huddlestonberry. comEngineering & Testing, LLC
March 25,2025
Project#0 1303-01 09
Clayton Homes
671 23 Road
Grand Junction, Colorado 81505
Attention: Ms. Karen Gonzalez
Subject OWTS Design
279 Mohawk Drive
Silt, Colorado
Dear Ms. Gonzalez,
At your request, Huddleston-Berry Engineering & Testing,LLC completed design of an Onsite
Wastewater Treatment System (OWTS) for an Accessory Dwelling Unit (ADU) at 279 Mohawk
Drive in Silt, Colorado. The site location is shown on Figure I - Site Location Map. A site plan
is included as Figure 2.
Site Description
At the time of the investigation, the southeastern portion of the site was occupied by an existing
residence and garage. The remainder of the site was open with undulating terrain. Topography
in the vicinity of the proposed ADU and OWTS is shown on Figure 2. Yegetation across the site
included grasses, weeds, brush, and trees. The site was bordered to the north, west, and east by
rural residential properties, and to the south by a rural residential property and Mohawk Drive.
Subsurface Investigation
In order to evaluate the site soils for onsite wastewater treatment, two test pits were excavated in
the vicinity of the Soil Treatment Area (STA). Using visual-tactile classification methods, the
soil profile consisted of 1.0 foot of topsoil above tan to brown, moist, stiff, structureless loam to
a depth of 4.0 feet. These soils are consistent with Soil Type 2A.
Below the loam, tan to brown, moist, stiff to very stiff lean with gravel and cobbles and weak
granular structure extended to the boffoms of the test pits. These soils contained less than 35o/o
rock and are consistent with Soil Type 24.
Groundwater was not encountered in the subsurface at the time of the investigation. In general,
based upon the results of the subsurface investigation, HBET believes that the seasonal high
groundwater elevation is deeper than 6.0 feet below the existing grade at this site.
The locations of the test pits are shown on Figure 2. Copies of the test pit logs are included in
Appendix A.
279 Mohawk Drive
#01303-0109
03t25t25
Onsite Wastewater Treatment Svstem
Huddleston-Berry
Eogit.dng&Tc$ing,lIC
Seepage Bed Design
The design of the absorption system generally follows the requirements of the Garfield County
Department of Public Works as outlined in the Garfield County On-Site Wastewater Treatment
System Regulations, effective July 2018. The proposed construction at the site is anticipated to
include a two-bedroom ADU.
Based upon the visual tactile classification of the soils, a Long-Term Acceptance Rate (LTAR)
of 0.5 will be utilized for the absorption field design. Infiltrator Systems Quick4 Standard
Chambers are proposed. Due to site topography, serial distribution is proposed. The daily flow
of the sewage disposal system is calculated below and a plan and profile of the absorption system
are shown on Figure 3.
Average Daily Flow: (4 persons)(75 GPD/person)
:300 GPD
Soil Treatment Area: (300 GPD / 0.5): 600 Square Feet
Adjusted Soil Treatment Area: (600 SFXl.0X0.7) :420 Square Feet
# of Quick4 Chambers : (420 I 121 :35 Chambers; Use 36 Chambers
System Installation
The installation of the septic tank, plumbing lines, Infiltrators, etc. should be completed in
accordance with the Garfield County On-Site Wastewater Treatment System Regulations and
Infiltrator Systems, Inc. specifications. In addition, the following construction procedures are
recommended:
' The septic tank and distribution box should be placed level over native soils that have
been scarified to a depth of 8 to 12 inches, moisture conditioned, and recompacted to
a minimum of 95Yo of the standard Proctor maximum dry density, within +2o/o of
optimum moisture content. However, up to 3-inches of washed rock or pipe bedding
passing the l-inch sieve may be used as a leveling course under the septic tank andlor
distribution box.
' The bottoms of trenches and backfill around the septic tank and distribution box
which will support sewer or effluent lines should be compacted to at least 90 percent
of the standard Proctor maximum dry density, within +2Yo of optimum moisture
content. Pipe bedding should have a maximum particle size of 1-inch.
' Vehicular or heavy equipment traffic and placement of structures should not encroach
within 10 feet of the septic tank or distribution box.
Inspection Schedule
Huddleston-Berry Engineering & TestingLLC should be retained to monitor the construction of
the OWTS. The following schedule of observation andlor testing should be followed:
' Observe the absorption bed excavation prior to placement of Infiltrator chambers.
' Observe placement of the septic tank, distribution box, and all connecting sewer and
effluent lines prior to backfill. Verify proper fall between inverts.
2212008 ALL PROJECTS\01303 - Clayton Homes\01103-0109 279 Moharvk DriveV00 - ceo\01303-0109 OWTSO32525.doc
279 Mohawk Drive
#01303-0109
03t25t25
Huddleston.Berry
Engiil..rtu8& T!{ing. l-tc
. Observe and verify installation of the absorption trenches prior to placement of cover
and backfill.
In conformance with Garfield County regulations, HBET will be required to provide Garfield
County with documentation certifying that the OWTS was placed in conformance to the plan and
profile and Garfield County regulations.
General Notes
The OWTS design was based upon the results of the subsurface investigation and on our local
experience. The design is valid only for the proposed construction.
We are pleased to be of service to your project. Please contact us if you have any questions or
comments regarding the contents of this report.
Respectfully Submitted:
Huddleston-Berry Engineering and Testingn LLC
Michael A. Berry, P.E.
Vice President of Engineering
JZ:\2008 ALL PROJECTS\O1303 - Clayton Homes\o1303-0109 279 Mohawk Drive\200 - Geo\01103-0109 OWTS032525.doc
FIGURES
F'IGURE 1
Site Location Map
OVERALL SITE PLAN
SCALE: l" = 150'
ENLARGED VIEW
SCALE: 1" = 30'
C.I. :2 FT
A TESTPIT
.T
NEW
AREA
+NEW ST
NEW TANK
RESIDENCE
NEW
WATERLINE-.L
I
AREA
// NEw
NEW WATERLINE
ADU
_l
Huddleston-Berry
Engineaing & Testing, LLC
2789 Riverside Parkway
Grand Junction, CO 81501
Project No.: 01303-0109
Datet 03125125
By: MAB
279 MOHAWK DRIVE
PARCEL#217914300017
ruE: INKN0 *0 L@AIoNSAPROXMiE ND MAy$tfr SOMa DURNG
CESTRUCNd BNED UPON Sre T@6WHY. M* MffiWE AND]OR
OTHER FACTORS S LSG AS PTqBLE SEBCKSSE Mf,. ACIUA L@NON
OF TM AND BS WU 8E INOI$TO ON A$UIL' DMWN6.-FIGURE2-SITEPLAN
GENERALTZED SYSTEM PROFILE
NOT TO
SCALE
DETAIL AREA
SCALE: l"=20'
1,0 FT xr[
ON EFFLUENT
RISERS (AS NECESSARY)
SUCH THAT LII)S ARE ATIR A4ryE FINISH GRAIE
EST. E.O FT
4,0 FT XAX.
ITfILTRATOR
BDXES
RESIDENTIAL
STRUCTURE CLEANOUT
EST. 6,0
TII 8,0 FT
2 COMPARMM SEPNCTAM ROM CDPM
APPROWD TAM LIST
INSTAIL ROWS OF INFILTMTORS IN
LEI'EL TRENC1TES FOLLOWING GROI,'}.ID
CONTOURS
**2 FT BELOW EXISTING
GRADEMAX**
I,O FT MIN. CBVER
FILTER
IN EUTLET TEE
TRATOR SYSTEMS QUICK4
STANDARD CHAMBERS
TANKWITH
4-INCH DIAME'IER SEWER AND
EFFLTJENT PIPE MEETTNG ASTM DI 7E5.
SCI{EDULE 40 OR SDR 35
GENERALIZED BED PROFILE
NOT TB
SCALE
i rGerlreni^ae^ ollc-r.rsols Jo-un rx:e rp.r-Niu-rs - _-.l
: FOLLOWINGCONTOURS. 4ROWSOF9OUTCK4STANDARD Ii,Y,lT{Tloi :xry:Ygl.yr lqtlT T"l:Ll
COVER SOIL; NATIVE SOILS OR OTHER SUITABLE
TOPSOIL. CRADE TO CARRY STJRFACE WATER
AWAY FROM
INFILTRATOR SYSTEMS QUICK4
FIBELOWDOSTING
GRADE MAX**
NEEDLE PLNCTIED. GEOTEXTILE
FABRIC IMMEDIATELY ABOVE CHAMBERS
6 FT MIN BETWEEN TRENCHES
MINIMUM I,OOO
GALLON CAPACITY
*'usE swEEP 90's oR
TWO 45'S AT 90
BENDS**
279 MOHAWK DRIVE
PARCEL#217914300017
FIGURE3-SEPTICSYSTEM
DETAILS
MINIMUM SBTBACKS
(UNITS = FT)
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WATERLINE
Huddleston'Berry
Enginwring & Testing, LLC
2789 Riverside Parkway
Grand Junction, CO 81501
Project No.: 01303-0109
Datet 03/25/25
By: MAB'*OTHER SETBACKS NOT LISTED HERE SHOULD BE IN ACCORDANCE WITH GARFIELD COT]NTY OWTS REGULATIONS
APPENDIX A
Typed Test Pit Logs
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